High mobility of sexually active population continues to be a risky factor for the spread of STIs and HIV, both in the source and destination sites. This paper analyses the social and cultural determinants for the spread of STIs and HIV along road construction sites which harbour a number of migrant workers from rural and urban areas. The study adopted a cross-sectional study design, using a structured questionnaire for respondents, a checklist for key informants and a guide for focus group discussants. A total of 308 respondents, including eighteen key informants and 20 focus group discussions were involved. Descriptive statistical analysis was employed for quantitative data whereas ethnographic content analysis was used for qualitative data. It was found that the level of knowledge about HIV/AIDS, how the disease spreads and the prevention methods was generally high. However, a corresponding change in sexual behavioural response was low. Many respondents still practise risky sexual behaviour, have many sexual partners and are inconsistent in using condoms. Some misconception about HIV/AIDS spread were also found. Also, there are many incidences of gender based violence which are under reported. Social and cultural factors responsible for the spread of HIV/AIDS include low risk perception and marital instability. It is recommended to the government and NGOs to involve and support local organizations for capacity building against HIV.